In the industrial field, the selection of sealing materials is crucial for the stable operation of equipment. Expanded graphite packing, as a common sealing material, has been favored by many enterprises due to its unique performance and wide range of applications. This article will explore in depth the advantages, disadvantages, and precautions in the installation and use of expanded graphite packing, helping you better understand and apply this material.
Expanded graphite packing, also known as flexible graphite packing, is made by core-weaving flexible graphite yarns. This material not only retains the excellent chemical properties of natural flake graphite but also adds many unique mechanical properties. Expanded graphite is a product obtained by chemically treating high-quality flake graphite and modifying it through high-temperature instantaneous expansion. It has the following characteristics:
Low Density and High Plasticity: The bulk density of expanded graphite is only 0.002–0.005 g/cm³, while the product density ranges from 0.8–1.8 g/cm³. This makes expanded graphite material not only lightweight but also highly plastic, allowing it to be processed into sealing products of various shapes.
High Purity: Expanded graphite has a fixed carbon content of up to 98%, and can even exceed 99%, meeting the sealing requirements of high-purity fields such as nuclear energy and aerospace.
Wide Temperature Range: Theoretically, expanded graphite can withstand temperatures from -200℃ to 3000℃. As a packing seal, it can be safely used within the temperature range of -200℃ to 800℃, resisting embrittlement and aging at low temperatures, and avoiding softening, deformation, or decomposition at high temperatures.
Chemical Corrosion Resistance: Expanded graphite has strong chemical inertness. Except for strong oxidants such as aqua regia, nitric acid, sulfuric acid, and halogens under certain temperatures, it can adapt to most media such as acids, alkalis, salt solutions, seawater, steam, and organic solvents.
Good Thermal Conductivity and Low Thermal Expansion Coefficient: The thermal conductivity and thermal expansion coefficient of expanded graphite are on the same order of magnitude as those of the mating materials of common sealing devices. This means it can maintain good sealing performance even under high temperature, cryogenic, or rapid temperature change conditions.
Radiation Resistance: Expanded graphite can withstand long-term exposure to neutron rays, γ-rays, α-rays, and β-rays without significant changes.
Low Permeability: Expanded graphite has high surface energy, easily forming a thin gas or liquid film, effectively preventing medium penetration.
Self-Lubricating: Expanded graphite retains a hexagonal planar layered structure. Under external force, the layers easily slide relative to each other, producing a self-lubricating effect, effectively preventing wear of shafts or valve stems.
Ease of Processing: Expanded graphite has very low hardness, can be cut with ordinary tools, and can be wound or bent freely.
Given these characteristics, expanded graphite packing has become an ideal sealing material with wide applicability and strong sealing capability, widely used in various industrial fields.
Before delving deeper into expanded graphite packing, let's first understand why it stands out among many sealing materials. Next, we will explore its unique advantages:
Good Self-Lubrication and Thermal Conductivity: The self-lubricating property of expanded graphite packing can effectively reduce friction with shafts, thus reducing wear and prolonging equipment service life. At the same time, good thermal conductivity helps transfer heat quickly, preventing local overheating and further protecting the equipment.
Low Friction Coefficient and High Versatility: Due to its low friction coefficient, expanded graphite packing can deliver excellent sealing performance in different types of equipment and pipelines, demonstrating strong versatility.
Good Softness and High Strength: This packing is not only soft, able to adapt to sealing components of various shapes and sizes, but also has high strength, capable of withstanding certain pressure and tensile forces.
Protection for Shafts: Its self-lubrication and softness work together to effectively prevent wear and corrosion of shafts, protecting their integrity.
High Customizability: According to different sealing requirements, expanded graphite packing can be reinforced with materials such as carbon fiber, copper wire, 304, 316L stainless steel, or Inconel wire, to meet higher demands for corrosion resistance and high-temperature resistance.
Although expanded graphite packing has many advantages, there are also some shortcomings that need attention and handling in application:
Sealing Performance Not Completely Stable: Due to the material characteristics of expanded graphite packing, its sealing performance may change under different temperatures, pressures, and other conditions. Especially under harsh conditions such as high temperature and high pressure, its sealing performance is more easily affected, potentially causing leakage and other issues.
Shorter Service Life: Expanded graphite packing is susceptible to wear, aging, and other factors during use, resulting in a relatively shorter service life. In harsh environments, this effect is more pronounced, requiring more frequent replacement and increasing maintenance costs.
Difficult Installation and Maintenance: Installation and maintenance of expanded graphite packing require special tools and techniques. Improper operation may lead to insecure installation or damage to the packing, affecting the sealing effect. In harsh environments such as high temperature and high pressure, installation and maintenance require even more caution and professional operation.
Due to its excellent performance, expanded graphite packing is widely used in many industrial fields. For example, in the petroleum, chemical, power, and pharmaceutical industries, it is used for static and dynamic sealing at valve and pump connections, and pipeline joints. Whether in high-temperature, high-pressure steam pipelines or highly corrosive chemical transport systems, expanded graphite packing provides reliable sealing, ensuring safe equipment operation.
Although expanded graphite packing has many advantages, its performance largely depends on correct installation and maintenance. Improper installation or untimely maintenance can not only reduce sealing effectiveness but also cause equipment failure. Therefore, mastering proper installation and maintenance methods is crucial.
Before installing expanded graphite packing, a series of preparatory steps must be taken to ensure a smooth installation and reliable sealing performance:
Remove Old Packing: Carefully remove old expanded graphite packing using specialized tools such as a packing extractor. Avoid damaging the equipment during operation.
Clean the Stuffing Box: Thoroughly clean the stuffing box of the shaft/rod, removing all remnants of old packing and impurities. This step is critical to ensure good sealing of the new packing.
Inspect Shaft/Rod and Components: Carefully examine the shaft/rod for corrosion, dents, scratches, or excessive wear. Check other related components for burrs, cracks, or wear. Replace any significantly defective parts in time.
Failure Analysis: Inspect the old expanded graphite packing and analyze the causes of its failure. This helps understand factors contributing to early failure and avoid them in future use.
Measurement and Recording: Accurately measure parameters such as shaft/rod diameter, stuffing box bore and depth. If using a water seal ring, record the distance from the bottom to the top of the stuffing box.
Based on the recorded measurements, calculate the required cross-sectional area and number of packing rings. Ensure the packing meets the operational conditions of the system and equipment. Inspect the packing surface to ensure it is free of defects.
Prepare Tools: Common tools for installation include ring cutters for expanded graphite packing, torque wrenches or ordinary wrenches, safety helmets, internal and external calipers, lubricant for fasteners, mirrors, and packing extractors.
Install New Packing: Ensure the equipment and packing are clean before installation. Place packing rings into the stuffing box one by one, ensuring that the joints of each ring are staggered.
Pre-tighten Gland Nuts: Use fasteners to pre-tighten the gland nuts, ensuring the packing is securely installed. Apply force evenly during pre-tightening to avoid overly tight or loose sections.
Initial Adjustment: After installation, hand-tighten the gland nuts. Allow a higher leakage initially during the start-up phase. Gradually adjust the gland nuts to reduce leakage.
Stable Adjustment: When the leakage reaches an acceptable level, stop tightening the gland nuts. If the medium suddenly stops leaking, back off the gland nuts slightly and readjust to avoid overheating the packing.
Regular Checks: Within a few hours after tightening or replacement, check the gland adjustments again. If the gland cannot be further adjusted or the packing shows signs of damage, replace with new expanded graphite packing to ensure reliable sealing of the medium.
Expanded graphite packing plays an important role in industrial sealing due to its excellent performance. It not only has good self-lubrication, thermal conductivity, flexibility, and high strength but can also be customized according to different needs. However, it also has shortcomings, such as unstable sealing performance, relatively short service life, and difficult installation and maintenance. By fully understanding its characteristics and strictly following correct installation and maintenance methods, the advantages of expanded graphite packing can be maximized, and its drawbacks prevented from negatively affecting industrial production. In practical applications, choosing the appropriate expanded graphite packing and performing scientific installation and maintenance will effectively improve the sealing performance and operational efficiency of equipment, providing strong assurance for the safety and stability of industrial production. In short, expanded graphite packing is a high-performance sealing material that can deliver tremendous value in various industrial applications when used and maintained correctly.